The difference in concentration of hematoporphyrin derivative between normal epithelium, dysplastic epithelium, and invasive carcinoma will be investigated in the Syrian Golden Hamster. The ability of photoactive compounds to identify and treat severe epithelial dysplasia and squamous cell carcinoma in the larynx of pound dogs and patients with advanced squamous cell carcinoma will also be investigated. Laryngeal cancer will be induced by spraying the larynx of hamsters on ethanol as their sole liquid diet with benzopyrene. After cancer induction hematoporphyrin derivative will be given intraperitoneally. Forty-eight hours later the animals will be sacrificed and the larynx studied histologically. Laryngeal cancer will be induced in the dogs by giving weekly injections of 20-methylcholanthrene submucosally into one true vocal cord. The progression of carcinogenesis and the extent of the induced cancer will be determined clinically using microlaryngoscopy. After successful cancer induction hematoporphyrin derivative (HPD) will be given intravenously. Areas of fluorescence will be mapped and correlated to the clinical stage. Biopsies of fluorescent and non-fluorescent areas of the vocal cord with induced cancer will be compared. The endolarynx will then be treated using the argon dye laser. Six weeks later the cancer will be restaged and biopsied. Patients with advanced squamous cell carcinoma of the head and neck who are not candidates for standard therapy will be given HPD as part of an already approved phase I, phase II study. The ability of photoirradiation therapy with HPD to treat the primary lesion will be studied. In addition, the ability of HPD to localize and treat areas of field cancerization beyond the primary lesion will be investigated. Use of HPD may significantly enhance the detection of dysplasia and early cancer and provide a selective, repeatable therapeutic method.